Replace to use __BEGIN_DECLS and __END_DECLS (#938)

Summary:
Replace all use cases of
```
#ifdef __cplusplus
extern "C" {
#endif
...
#ifdef __cplusplus
}
#endif
```
with
```
__BEGIN_DECLS
...
__END_DECLS
```
keep its usage consistent in the project.

Pull Request resolved: #938

Reviewed By: kevin0571

Differential Revision: D27115606

Pulled By: cuva

fbshipit-source-id: b49fd9d3b88c0d77c12def1601ddf5d2eeb9f96e

Author: hanton

ComponentKit/LayoutComponents/CKComponentLayoutBaseline.h

@@ -10,21 +10,15 @@
 
 #import <Foundation/Foundation.h>
 
-#import <ComponentKit/CKDefines.h>
-
-#if CK_NOT_SWIFT
+#import <RenderCore/CKDefines.h>
 
 /**
  Set a key value pair using this in RCLayout.extra for a custom baseline. The component which uses this property should also override @{usesCustomBaseline} to return YES.
  e.g. @{kCKComponentLayoutExtraBaselineKey : 20}
  */
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+CK_EXTERN_C_BEGIN
+
 extern NSString *const kCKComponentLayoutExtraBaselineKey;
-#ifdef __cplusplus
-}
-#endif
 
-#endif
+CK_EXTERN_C_END

ComponentKitTestHelpers/CKTestRunLoopRunning.h

@@ -9,10 +9,9 @@
  */
 
 #import <Foundation/Foundation.h>
+#import <RenderCore/CKDefines.h>
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+CK_EXTERN_C_BEGIN
 
 /**
  Runs the current thread's run loop until the block returns YES or a timeout is reached.
@@ -21,6 +20,4 @@ extern "C" {
  */
 extern BOOL CKRunRunLoopUntilBlockIsTrue(BOOL (^block)(void));
 
-#ifdef __cplusplus
-}
-#endif
+CK_EXTERN_C_END

ComponentKitTests/CKComponentHostingViewTestModel.h

@@ -43,12 +43,8 @@ CK_INIT_UNAVAILABLE;
 
 @class CKComponent;
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+CK_EXTERN_C_BEGIN
 
 CKComponent *CKComponentWithHostingViewTestModel(CKComponentHostingViewTestModel *model);
 
-#ifdef __cplusplus
-}
-#endif
+CK_EXTERN_C_END

RenderCore/Utilities/CKWeakObjectContainer.h

@@ -9,20 +9,17 @@
  */
 
 #import <Foundation/Foundation.h>
+#import <RenderCore/CKDefines.h>
 
 @interface CKWeakObjectContainer : NSObject
 @property (readonly, nonatomic, weak) id object;
 + (instancetype)newWithObject:(id)object;
 @end
 
-#ifdef __cplusplus
-extern "C" {
-#endif
+CK_EXTERN_C_BEGIN
 
 extern void ck_objc_setNonatomicAssociatedWeakObject(id container, void *key, id value);
 extern void ck_objc_setAssociatedWeakObject(id container, void *key, id value);
 extern id ck_objc_getAssociatedWeakObject(id container, void *key);
 
-#ifdef __cplusplus
-}
-#endif
+CK_EXTERN_C_END